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Medical News

Experimental Microbicide Shows Small Level of Protection Against HIV for Women, Study Presented at CROI Indicates

February 10, 2009

Research has shown "a small amount of protection from a vaginal gel that acts by binding up the AIDS virus and preventing it from invading cells," according to a study presented Monday at the 16th Conference on Retroviruses and Opportunistic Infections in Montreal, Canada, the Washington Post reports (Brown, Washington Post, 2/10). The experimental microbicide, called PRO 2000 and manufactured by Indevus Pharmaceuticals, is designed to prevent HIV from attaching to certain white blood cells. According to the study -- which primarily aimed to test the gel's safety -- the PRO 2000 gel is 30% effective in preventing HIV infection. Although the findings are not statistically significant, the study is the first to demonstrate a possible beneficial effect from using microbicides. According to NIH, an effectiveness rate of 33% would be statistically significant.

For the NIH-funded study, Salim Abdool Karim of the Center for the AIDS Program of Research in South Africa and colleagues divided 3,100 women from Malawi, South Africa, the U.S., Zambia and Zimbabwe into four groups - one that used the PRO 2000 gel; a second that used ReProtect's microbicide gel BufferGel; the third that used a placebo gel; and the remaining group used no microbicide gel. All the women received counseling to encourage condom use (Stobbe, AP/, 2/9). At the conclusion of the 20-month study period, 194 women had contracted HIV, including 36 women from the PRO 2000 group, 54 from the BufferGel group, 51 from the placebo group and 53 from the group that used no microbicides.

According to NIH, participants reported use of the gels in 81% of sex acts. Kathy Stover, NIH communications officer, said the study was based on self-reporting, and therefore the researchers "have no way to verify that the gel was actually applied prior to sexual intercourse" (Reichard, CQ HealthBeat, 2/9). According to health officials, further research will be necessary to determine the gel's efficacy. London's Medical Research Council currently is conducting a study of the PRO 2000 gel involving 9,500 women, which is three times the size of the first study, Bloomberg reports (Lauerman, Bloomberg, 2/9).

Researchers for many years have worked to develop effective microbicides to prevent HIV transmission, but no earlier studies have shown promising results and two trials showed that the gels actually increased the risk of contracting HIV. According to the Post, microbicides have advantages over other HIV prevention methods because they can be applied without the knowledge of sexual partners. This is particularly important in places where cultural practices might limit a woman's ability to insist on abstinence or condom use (Washington Post, 2/10). Karim, who presented the PRO 2000 study at the conference, said, "while not conclusive, [it] provides a glimmer of hope to millions of women at risk for HIV, especially young women in Africa" (AFP/, 2/9).

PrEP with Antiretrovirals Shows Promise in Preventing Monkey Form of HIV
In related news, two additional CDC studies presented at CROI found that pre-exposure prophylaxis, or PrEP, with antiretroviral drugs administered by mouth or by vaginal gels were highly effective at protecting rhesus macaques from the simian version of HIV, or SIV, the Post reports.

For the first study, the researchers gave the monkeys oral doses of a compound containing the antiretroviral drugs tenofovir and emtricitabine, sold under the brand name Truvada. The researchers administered the drugs at different intervals -- called intermittent PrEP -- both before and after exposing the macaques rectally to SIV once weekly for three months. Of the monkeys that received the first dose one or three days prior to contact with the virus, five out of six were protected from SIV. Monkeys in all five treatment groups had significantly lower risk of infection compared with the untreated monkeys, and PrEP was most effective in preventing infection if administered one to seven days prior to exposure compared with immediately before exposure or only intermittently after exposure. According to Gerardo Garcia-Lerma, CDC epidemiologist and lead author of the study, tenofovir has a long active life in the body; however, it might take longer than two hours for the drug to enter the immune system and provide protection against the virus.

For the second study, the researchers tested vaginal gels containing either the combination drug or tenofovir alone. They applied the gel to macaques 30 minutes before twice-weekly exposure to SIV. According to the study's findings, all of the six monkeys that received the two-drug gel and all of the six monkeys that received the tenofovir-only gel were protected from the virus. Out of 11 macaques that received no gels, 10 contracted SIV after a median of four exposures to the virus (Washington Post, 2/10). The study's findings suggest that single-drug vaginal gel formulations are equally effective as combination-drug formulations in providing complete protection against SIV (CDC release, 2/9).

Walid Heneine -- laboratory chief of CDC's Division of HIV/AIDS Prevention, who led the second study -- said the results are "very promising, although we're waiting for the results of human trials to see if they correlate with animal studies." Warren added that results of the studies are "very exciting" but added that "we mustn't be too optimistic that we'll see the same results in people" (Bloomberg, 2/9). According to the Post, seven studies are currently underway to test the efficacy of Truvada and tenofovir as HIV prevention methods when administered daily. About 18,000 people from Botswana, Kenya, Thailand, the U.S. and Uganda are participating in the studies (Washington Post, 2/10).

Men Taking HAART Can Transmit HIV Through Semen
An additional two studies presented at the conference indicate that men who take highly active antiretroviral therapy may still transmit HIV to sexual partners through their semen, Reuters reports. For the studies, Prameet Sheth of the University of Toronto and Anne-Genevieve Marcelin of Pitie-Salpetriere Hospital found that men who had undetectable HIV viral loads in their blood still carried the virus in their semen. Sheth told reporters at the conference, "I would argue that it is infectious although we don't know what level of virus is required." According to the researchers, it is unclear why HAART can bring down viral loads to undetectable levels in the blood but not eliminate the virus from semen. (Reuters, 2/9).

Research Funding Aims at HIV Cure
Bloomberg recently examined the "offering [of] bounties to a new wave of scientists to wipe out HIV." The U.S. has asked researchers to create a program aimed at developing a cure for HIV/AIDS, and the Bill & Melinda Gates Foundation has offered $100,000 grants for research on permanently eliminating the virus from the body. According to Bloomberg, pressure to develop successful HIV/AIDS treatments has increased in recent years, following the 2007 failure of an experimental Merck vaccine and similar disappointments from vaginal microbicide trials.

According to Bloomberg, NIH has sought to fund proposals that will research how HIV remains in the body even after antiretrovirals reduce the viral load to undetectable levels. The Gates Foundation is seeking proposals with the same goal, according to Bloomberg. The persistence of HIV in the body is expected to be a major topic at CROI, according to Bloomberg. Anthony Fauci, director of NIH's National Institute of Allergy and Infectious Diseases, said it is "very easy" to reduce HIV loads to undetectable levels. "However, to knock it out, we'll either have to get true eradication, or get the reservoir of virus that's inside cells so low that it can't come back," Fauci said. He added that it might be possible to develop a "functional cure" for HIV that would allow the immune system to handle the virus without drugs, similar to remission for cancer (Lauerman, Bloomberg, 2/9).

Back to other news for February 2009

Reprinted with permission from You can view the entire Kaiser Daily HIV/AIDS Report, search the archives, or sign up for email delivery at The Kaiser Daily HIV/AIDS Report is published for, a free service of the Kaiser Family Foundation, by The Advisory Board Company. © 2009 by The Advisory Board Company and Kaiser Family Foundation. All rights reserved.

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This article was provided by Henry J. Kaiser Family Foundation. It is a part of the publication Kaiser Daily HIV/AIDS Report. Visit the Kaiser Family Foundation's website to find out more about their activities, publications and services.
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More News and Research on Microbicides

Please note: Knowledge about HIV changes rapidly. Note the date of this summary's publication, and before treating patients or employing any therapies described in these materials, verify all information independently. If you are a patient, please consult a doctor or other medical professional before acting on any of the information presented in this summary. For a complete listing of our most recent conference coverage, click here.